(i) Field of the Invention
The present invention relates to an up-converter used for frequency-converting an upward signal outputted from a terminal unit to an in-building upward signal in an in-building CATV system in which an external bi-directional CATV system transmission path and an in-building terminal are interconnected to transmit upward and downward signals in both directions. The present invention further relates to a down-converter for converting the frequency of the in-building upward signal transmitted from the side of the terminal unit via the up-converter to a transmission frequency in the bi-directional CATV system to transmit the signal onto the transmission path of the bi-directional CATV system.
(ii) Description of the Related Art
In a conventionally known in-building CATV system connected to a lead-in wire from an external bi-directional CATV system, a downward signal transmitted from a central apparatus of the bi-directional CATV system via the lead-in wire is transmitted to a terminal in the building via a transmission line in the building. Additionally, an upward signal inputted from the terminal unit is transmitted to the lead-in wire, and outputted toward the central apparatus of the bi-directional CATV system via the lead-in wire.
Moreover, in the in-building CATV system, noises generated in the building are superposed to the in-building transmission line via the terminal on the subscriber side, flow together, and are outputted to the external bi-directional CATV system together with the upward signal.
To reduce the confluent noises flowing out to the external bi-directional CATV system, in a heretofore proposed method, an up-converter is used to once frequency-convert the upward signal generated in the terminal unit such as a cable modem on the subscriber side, that is, the signal with a frequency band, for example, of 5 to 42 MHz which can be transmitted by the bi-directional CATV system to an upward signal (hereinafter referred to as the in-building upward signal) with a UHF band (e.g., 913 to 950 MHz) which is higher than the original frequency and which does not overlap and is much higher than the transmission frequency (e.g., 54 to 860 MHz) of the downward signal. The in-building upward signal is transmitted to the lead-in wire, and the down-converter is used to convert the frequency of the in-building upward signal to the original frequency, that is, the transmission frequency of the upward signal in the bi-directional CATV system, immediately before the upward signal is outputted to the lead-in wire via the in-building transmission line.
The up-converter for use in the conventional in-building CATV system is usually constituted as shown in FIG. 5A.
Specifically, first, the up-converter needs not only to frequency-convert the upward signal outputted from the terminal unit to the in-building upward signal, but also to output the downward signal transmitted via the transmission line of the in-building CATV system toward the terminal unit. For this purpose, in the conventional up-converter, in order to form two upward and downward paths in the up-converter, the up-converter is provided with distribution circuits SP1 and SP2, and a first terminal Tin connected to the terminal unit on the subscriber side and a second terminal Tout connected to the in-building CATV system are connected to the distribution circuits SP1 and SP2, respectively.
Moreover, the upward signal inputted to the first terminal Tin from the terminal unit is inputted to a frequency converter 94 via a low-pass filter (hereinafter referred to as LPF) 92 which is connected to one distribution terminal of the distribution circuit SP1. Furthermore, the in-building upward signal outputted from the frequency converter 94 is inputted to one distribution terminal of the distribution circuit SP2 connected to the second terminal Tout via a high-pass filter (hereinafter referred to as HPF) 96, and then outputted to the transmission line of the in-building CATV system from the second terminal Tout via the distribution circuit SP2.
Furthermore, the downward signal transmitted to the second terminal Tout is transmitted from the other distribution terminal of the distribution circuit SP2, via a downward signal transmitting path provided with an LPF 98, to the other distribution terminal of the distribution circuit SP1. Then, the downward signal is outputted to the terminal unit on the subscriber side from the first terminal Tin via the distribution circuit SP1.
Additionally, the LPF 92 disposed in the previous stage of the frequency converter 94 selectively passes the upward signal from the side of the terminal unit, the HPF 96 disposed in the subsequent stage of the frequency converter 94 selectively passes the in-building upward signal outputted from the frequency converter 94, and the LPF 98 disposed on the downward signal path selectively passes the downward signal.
However, in the conventional up-converter constituted as described above, since the upward signal path provided with the frequency converter 94 and the downward signal path are separated using the distribution circuits SP1, SP2, there is a problem that signal losses are increased when the signals pass through the distribution circuits SP1, SP2.
Moreover, the upward signal inputted to the first terminal Tin from the terminal unit is not only transmitted to the frequency converter 94 through the LPF 92, but also outputted onto the transmission line of the in-building CATV system from the second terminal Tout through the LPF 98 which allows to pass low frequency signals. This adversely affects the operation of a bi-directional amplifier disposed on the transmission line of the in-building CATV system as shown in FIG. 5B.
Specifically, the downward signal and the in-building upward signal are to be transmitted by the in-building CATV system provided with the down-converter. Even when the upward signal different in frequency from these signals is transmitted to the transmission line of the in-building CATV system from the up-converter, no problem basically arises. However, when the bi-directional amplifier is disposed on the transmission line of the in-building CATV system, as shown in FIG. 5B, the in-building upward signal and the downward signal are amplified by amplification circuits AMP 1, AMP 2 provided with HPF, LPF for signal selection both in previous and subsequent stages, respectively. In this constitution, the upward signal outputted from the up-converter is inputted to the output side of the amplification circuit AMP 2 for amplifying the downward signal. When the upward signal is inputted in this manner, the upward signal turns to the input side of the amplification circuit AMP 2 via the feedback circuit of the amplification circuit AMP 2, and the amplification circuit AMP 2 oscillates.
Furthermore, the down-converter for use in the conventional in-building CATV system is usually constituted as shown in FIG. 6A.
Specifically, first, the down-converter needs not only to frequency-convert the in-building upward signal transmitted from the terminal side via the in-building transmission line to the upward signal with a lower frequency, but also to transmit the downward signal inputted from the bi-directional CATV system via the lead-in wire onto the in-building transmission line. For this purpose, in the conventional down-converter, in order to form two upward and downward paths in the down-converter, the down-converter is provided with distribution circuits SP3 and SP4, and an external connection terminal T4 connected to the lead-in wire from the bi-directional CATV system and an internal connection terminal T3 connected to the in-building transmission line are connected to the distribution circuits SP4 and SP3, respectively.
Moreover, the in-building upward signal inputted to the internal connection terminal T3 is outputted to a frequency converter 194 via an HPF 192 which is connected to one distribution terminal of the distribution circuit SP3. Furthermore, the frequency-converted upward signal outputted from the frequency converter 194 is outputted to one distribution terminal of the distribution circuit SP4 connected to the external connection terminal T4 via an LPF 196, and then outputted to the transmission line of the external bi-directional CATV system from the external connection terminal T4 via the distribution circuit SP4.
Furthermore, the downward signal inputted to the external connection terminal T4 is transmitted from the other distribution terminal of the distribution circuit SP4, via a downward signal transmitting path provided with an HPF 198, to the other distribution terminal of the distribution circuit SP3. Then, the downward signal is outputted onto the in-building transmission line from the internal connection terminal T3 via the distribution circuit SP3.
Additionally, the HPF 192 disposed in the previous stage of the frequency converter 194 selectively passes the in-building upward signal, the LPF 196 disposed in the subsequent stage of the frequency converter 194 selectively passes the frequency-converted upward signal outputted from the frequency converter 194, and the HPF 198 disposed on the downward signal path selectively passes the downward signal.
However, in the conventional down-converter constituted as described above, the upward signal path provided with the frequency converter 194 and the downward signal path are separated using the distribution circuits SP3, SP4. Therefore, a problem arises that signal losses are increased when the signals pass through the distribution circuits SP3, SP4.
Moreover, the in-building upward signal inputted to the internal connection terminal T3 is not only inputted to the frequency converter 194 through the HPF 192, but also outputted onto the transmission line of the external bi-directional CATV system from the external connection terminal T4 through the HPF 198. This adversely affects the operation of a bi-directional amplifier disposed on the transmission line of the external bi-directional CATV system as shown in FIG. 6B.
Specifically, the downward signal and the upward signal with a lower frequency than that of the downward signal are to be transmitted in the external bi-directional CATV system. Even when the in-building upward signal different in frequency from these signals is transmitted onto the transmission line of the external bi-directional CATV system from the down-converter, no problem basically arises.
However, the bi-directional amplifier for amplifying the upward and downward signals flowing through the transmission path is disposed on the transmission line of the bi-directional CATV system. As shown in FIG. 6B, the upward and downward signals are amplified by amplification circuits AMP 3, AMP 4 provided with LPF, HPF for signal selection in the previous and subsequent stages, respectively. In this constitution of the amplifier, the in-building upward signal passed through the down-converter is inputted to the output side of the amplification circuit AMP 4 for amplifying the downward signal. When the in-building upward signal is inputted in this manner, the in-building upward signal turns to the input side of the amplification circuit AMP 4 via the feedback circuit of the amplification circuit AMP 4, and the amplification circuit AMP 4 oscillates.
Wherefore, an object of the present invention is to provide an up-converter for use in frequency-converting an upward signal from a terminal unit to an in-building upward signal to an in-building CATV system for transmitting signals in two opposite directions between an external bi-directional CATV system and the terminal unit in a building, which reduces signal losses and which exerts no influence on other apparatuses such as a bi-directional amplifier.
Another object of the present invention is to provide a down-converter in an in-building CATV system for transmitting signals in two opposite directions between the external bi-directional CATV system and a terminal unit in a building and for use in frequency-converting an in-building upward signal transmitted from a terminal side via an in-building transmission line to an upward signal for an external bi-directional CATV system, which reduces signal losses and which exerts no influence on the operation of a transmission apparatus on the side of the bi-directional CATV system.
To attain this and other objects, according to one aspect of the present invention, there is provided an up-converter for an in-building CATV system, which frequency-converts an upward signal inputted to a first terminal from the side of a terminal unit to an in-building upward signal using a frequency converter, subsequently outputs the in-building upward signal onto a transmission line of the in-building CATV system from a second terminal, transmits a downward signal inputted from the second terminal to the first terminal via an internal downward signal path, and outputs the downward signal toward the terminal unit from the first terminal, in which:
(1) a low-pass filter is disposed between the first terminal and the frequency converter to cut off the input of the downward signal passed through the downward signal path, and to selectively pass the upward signal from the side of the terminal unit;
(2) a high-pass filter is disposed between the frequency converter and the second terminal to cut off the downward signal inputted from the second terminal, and to selectively pass the in-building upward signal outputted from the frequency converter;
(3) the low-pass filter is disposed between the second terminal and the downward signal path to cut off the input of the in-building upward signal outputted from the frequency converter, and to selectively pass the downward signal inputted from the second terminal; and
(4) the high-pass filter is disposed between the downward signal path and the first terminal to cut off the upward signal inputted from the first terminal, and to selectively pass the downward signal.
As a result, only the downward signal is outputted on the side of the terminal unit from the up-converter of the present invention, and only the in-building upward signal frequency-converted in the frequency converter is outputted onto the transmission line of the in-building CATV system. Since the non-converted upward signal outputted from the terminal unit is not transmitted to the transmission line of the in-building CATV system, the operation of transmission apparatuses such as the bi-directional amplifier disposed on the transmission line can be prevented from being adversely affected.
Moreover, in the present invention, the upward and downward signal paths in the up-converter are separated by the four types of filters. Different from the conventional apparatus shown in FIG. 5A, no distribution circuit for separating the signal path is used. Therefore, the signal losses in the up-converter can be reduced.
Here, as is known, in the frequency converter, by mixing a reference signal with a predetermined frequency and the upward signal, the upward signal is frequency-converted to an upward signal with a frequency which is higher than that of the upward signal, more especially, the downward signal. Moreover, as the reference signal for use in the frequency conversion by the frequency converter, the reference signal generated in an oscillation circuit incorporated in the up-converter may be used.
In this case, however, the reference signal on the side of the up-converter does not correspond to the reference signal on the side of the down-converter which frequency-converts the in-building upward signal to the upward signal. On the side of the down-converter, the in-building upward signal cannot be converted to the upward signal for the external bi-directional CATV system.
To solve such problem, according to the present invention, the frequency converter may be constituted to use the reference signal with the predetermined frequency superposed to the downward signal transmitted from the in-building CATV system, and to frequency-convert the upward signal to the in-building upward signal. In this manner, the reference signal on the side of the up-converter corresponds to the reference signal on the side of the downward signal. Moreover, the in-building upward signal can accurately be converted to the upward signal for the external bi-directional CATV system in the down-converter.
Additionally, as the above-described reference signal, a pilot signal for use in level adjustment of the downward signal in the external bi-directional CATV system, or a reference signal generated and outputted to the in-building transmission line by the down-converter may be used.
On the other hand, when the frequency converter is constituted to utilize the reference signal with the predetermined frequency superposed to the downward signal transmitted from the in-building CATV system, and to frequency-convert the upward signal to the in-building upward signal, the reference signal needs to be inputted to the frequency converter in the up-converter.
For this purpose, a part of the downward signal inputted to the second terminal from the in-building transmission line may be branched to the frequency converter. However, when such a branch device is disposed on the signal path leading to each filter from the second terminal, not only the downward signal but also the in-building upward signal pass through the branch device. The signal loss of the in-building upward signal occurs in the branch device.
Therefore, according to the present invention, this branch device may be disposed on the downward signal path to which the downward signal is inputted from the second terminal via the low-pass filter, so that a part of the downward signal inputted via the low-pass filter may be inputted to the frequency converter. Specifically, the reference signal superposed to the downward signal may be inputted to the frequency converter without influencing the in-building upward signal.
According to another aspect of the present invention, there is provided a down-converter for an in-building CATV system, which outputs a downward signal inputted to an external connection terminal from a lead-in wire onto a transmission line in a building from an internal connection terminal via a downward signal path, frequency-converts an in-building upward signal inputted to an internal connection terminal from the transmission line to an upward signal for an external bi-directional CATV system using a frequency converter, and subsequently outputs the upward signal onto a transmission path of the external bi-directional system from an external connection terminal via the lead-in wire, in which:
(1) a high-pass filter is disposed between the internal connection terminal and the frequency converter to cut off the input of the downward signal passed through the downward signal path, and to selectively pass the in-building upward signal;
(2) a low-pass filter is disposed between the frequency converter and the external connection terminal to cut off the downward signal inputted from the external connection terminal, and to selectively pass the upward signal outputted from the frequency converter;
(3) the high-pass filter is disposed between the external connection terminal and the downward signal path to cut off the input of the upward signal outputted from the frequency converter, and to selectively pass the downward signal inputted from the external connection terminal; and
(4) the low-pass filter is disposed between the downward signal path and the internal connection terminal to cut off the in-building upward signal inputted from the internal connection terminal, and to selectively pass the downward signal.
As a result, only the downward signal is outputted to the transmission line in the building from the down-converter of the present invention, and only the upward signal frequency-converted in the frequency converter is outputted onto the transmission line of the external bi-directional CATV system. Moreover, since the in-building upward signal is not transmitted to the transmission path of the external bi-directional CATV system, the operation of transmission apparatuses such as the bi-directional amplifier disposed on the transmission path can be prevented from being adversely affected.
Moreover, in the present invention, the upward and downward signal paths in the down-converter are separated by the four types of filters. Different from the conventional apparatus shown in FIG. 6A, no distribution circuit for separating the signal path is used. Therefore, the signal losses in the down-converter can be reduced.